A two-door sports car, the Honda S2000 has an inline four-cylinder engine with 237 horsepower, which is paired with a six-speed manual transmission. The Infiniti G20 has twice as many doors (four) and although it has a four-cylinder engine as well, it is considerably less powerful. Also, its standard transmission is a five-speed manual instead of a six-speed.
Honda discontinued the S2000 in 2009, thus ending its decade-long production run. Nissan discontinued the Infiniti G20, as well, although the company replaced it with the G35, a rebadged rear-wheel-drive Nissan Skyline that debuted in the United States for the 2003 model year.
According to Kelley Blue Book, the value range of the Honda S2000 is around $9,900 to $34,000, as of August 2010. For the Infiniti G20, the value range is much lower: at around $1,800 to $7,200.
The Honda S2000 and Infiniti G20 are vehicles from Honda and Nissan's luxury brand Infiniti, respectively. They are completely different vehicles. The former is a roadster, and the latter is a luxury sedan.